THE MUSCULAR SYSTEM 1-5 The dorso-epitrochlearis* is a climbing muscle, present in all Apes, but represented by fascia in Man. It arises from the latissimus dorsi at the junction of the muscle and tendon, and it is inserted into the internal intermuscular septum. Fibres may pass into it from the coraco-brachialis. It is innervated by the musculo-spiral nerve, so it is not a part of the latissimus dorsi, which is supplied by the middle subscapular nerve. Although it is a climbing muscle I have seen it larger in the Drill than in purely arboreal Monkeys (174). The triceps is a powerful muscle in all the Apes. The outer and inner heads are as in Man; but the long head is more extensive, arising over an area extending from the border of the glenoid cavity to as far as the middle of the axillary border of the scapula. That extent includes the various individual conditions. It is inserted into the tip and dorsum of the olecranon process ; and a bursa may lie between it and the bone. The anconens is present in all, but the subanconeus is inconstant. The palmaris longns is present or absent in one or both arms. It runs from the common flexor origin from the internal condyle of the humerus to the palmar fascia or the upper border of the synovial sheath of the flexor sublimis and flexor profundus digitorum. The pronator radii teres has no coronoid head in the Gorilla and Gibbon, but it is present in the Orang and Chimpanzee. In the latter the condylar head is fused with the flexor carpi radialis, and the coronoid head with the flexor sublimis digitorum. Some fibres spring from the internal intermuscular septum. The median nerve passes * Groonroos (75) has dealt with these muscles.